How to Write Apartment Numbers in an Address
For U.S. mailing addresses, USPS Publication 28 specifies recognized secondary-unit designators such as APT and gives placement rules for apartment information. This guidance is explicitly U.S.-postal. International address formats can follow different national standards and should not be forced into USPS form.
For U.S. postal addresses, include the appropriate secondary-unit designator and apartment identifier on the delivery-address line in USPS-compatible form.
Key details
Important caveats
Scope Boundary
This guidance is explicitly U.S.-postal. International address formats can follow different national standards and should not be forced into USPS form.
Further guidance
Recommendation
For U.S. postal addresses, include the appropriate secondary-unit designator and apartment identifier on the delivery-address line in USPS-compatible form.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Publication 28, section 213: Secondary Address Unit Designators (opens in a new tab)United States Postal Service · Official U.S. postal guidance for apartment and secondary unit designators